The truth is that your chosen message will be a major factor in whether your ex partner will call you back or not. You want them to return your phone call / text message / IM, so listen up because I'm going to give you the scoop on the magic words to say that will have them dialling you back very quickly.
But before we get to what you should say, let's first have a look at what you need to avoid.
There are two ways that everyone seems to do, but are best avoided if you want to repair your relationship. They are the message where you plead for your ex to call you back or tell them that they need to call back because of an emergency.
I'm sure you don't need me to tell you that both approaches can put you in a worse position than you started from and could potentially damage any further communication that you have with your ex, so even though you might be frustrated that they won't call you, these approaches will not work.
The best thing to do is combine both curiosity and self interest as combined they pack a powerful force.
The two combined create a powerful and compelling desire for them to wonder what you mean, and they will be thinking about it all day until they can't wait a moment longer, they need to find out what you are talking about.
Let's have a quick look at an example so I can show you what I mean.
In your best friendly tone say something like ... "Hi Barbara, it's David here, Just a quick call to let you know how much I appreciated what you did for me. Give me a call because I want to thank you in person."
Barbara is probably wondering right now what she did that you appreciated (curiosity), and will also feel good because it's such a positive message (self interest).
Of course, you will need to have worked out beforehand what that 'thing' was that you appreciated so much. It should be something believable and real although it doesn't need to be anything big, small things are fine as well.
If they do call, (and they probably won't be able to resist), then keep the conversation light and friendly. Keep the call short and make sure you remain happy and positive no matter how frustrated you really are.